This type of roller conveyor is known and is disclosed for example in U.S. Pat. No. 4,488,639. This conventional roller conveyor includes a number of free rollers capable of only free rotation disposed on a main frame to define a transfer path, and a support frame associated with the main frame. The support frame is provided with pins extending parallel to and below the roller axes, each of said pins being provided with a wheel and a sprocket, said wheel and sprocket being rotatable integrally and said wheel being simultaneously contactable with a pair of adjacent free rollers. A driving chain guided along said main frame is engaged with the sprockets.
According to this conventional type, the wheels are rotated by the driving chain through the sprockets, and the 25 rotation of each wheel is transmitted to the pair of free rollers contacted therewith, so that objects to be transferred are transferred on the transfer path by the rotation of the free rollers groups.
According to such conventional type, since the free rollers are stationary with respect to the main frame, the roller pitch cannot be changed according to the shape and length of objects to be tansferred and the conveyor system becomes expensive when the roller pitch is reduced so as to smoothly transfer objects of minimum shape and length. Similarly, since the support frames are stationary, a large number of them are required.